Hybrid vehicle drive system having a drive mode using both engine and electric motor

A hybrid drive system for a motor vehicle, comprising:

• an engine operated by combustion of a fuel;
• an electric energy storage device for storing an electric energy;
• an electric motor operated with the electric energy stored in said electric energy storage device;
• normal drive control means for controlling said engine and said electric motor so as to establish a normal drive state in which one of said engine and said electric motor is operated as a drive power source to drive the motor vehicle;
• power drive control means for controlling said engine and said electric motor so as to establish a power drive state in which there is available a power drive mode in which both of said engine and said electric motor are operated as the drive power source to drive the motor vehicle;
• power drive selecting means manually operated by an operator of the motor vehicle when the operator desires to drive the motor vehicle in said power drive mode;
• and
• power drive restricting means for permitting said power drive control means to establish said power drive state if said power drive selecting means is not manually operated, and inhibiting said power drive control means from establishing said power drive state, to thereby inhibit the motor vehicle from being driven in said power drive mode, if said power drive selecting means is not manually operated.